1. Field of the Invention
The present invention relates to automatic transmissions for automotive vehicles, and, more particularly, it pertains to a continuously ratio-varying transmission (CVT) unit of the toroidal race-rolling traction type with a split variator AWD traction.
2. Description of the Prior Art
Continuously variable transmissions of the toroidal race-rolling traction type are well known. CVTs of this type provide a continuously variable range of transmission ratios through the arrangement of possibly more than one epicyclic gear train. The engine drive variator has an output disc that delivers power to an epicyclic gear train that is also driven by an output shaft. More specifically, a variator output disc directly drives a sun gear of a planetary gearset.
CVT units of the toroidal race-rolling traction type wherein the output disc directly drives a sun gear of a planetary gearset are described in U.S. Pat. No. 4,756,211, EP Document 84,724, U.K. Patent 1,228,749, and U.K. Patent 2,136,893.
Multiple planetary gearsets incorporating a CVT transmission of the toroidal type is described in U.S. Pat. No. 4,768,398. The drive system described there includes two epicyclic gearsets. A first gearset provides a compound planet system by way of a second set of gears in the system. The annulus of the first epicyclic gearing provides drive to a final drive shaft and provides reverse drive by way of a second set of gears. Depending on the variator ratio, the first epicyclic gearing provides a forward speed, neutral or a reverse speed in low regime. The annulus of the second epicyclic gearing provides drive to the final drive shaft in high regime. This method, as well as those of the other mentioned patents, offer complex methods of gearset arrangement and application of the variator to gearset relationship.
It is therefore desirable to create a simpler but just as effective drive method.